The present invention generally relates to a storage system and a management method of its storage medium, and can be suitably applied to a storage system having a storage medium and an internal network for connecting such storage medium, and a management method of its storage medium.
With a storage system, storage mediums such as a plurality of hard disk drives (HDD) are connected to a storage controller to configure one large storage apparatus. By connecting a plurality of storage mediums, data can be made redundant in addition to being able to provide a large capacity, and availability can be improved thereby. RAID (Redundant Arrays of Inexpensive Disks) and the like are known as this kind of technology. In addition, as technology for providing a connection method of multiple storage mediums, there is SCSI as an interface that connects based on the bus system, or a fibre channel as an interface capable of forming a network on the topology of a fabric or a loop. In order to realize high availability of a storage system, not only is the redundancy of the storage medium to store data important, the redundancy of the network that connects the storage medium to the storage controller and enables access is also important. For example, Japanese Patent Laid-Open Publication No. 2001-222385 describes technology for improving the redundancy in a case of connecting hard disks with a fibre channel arbitrated loop configuration.
In addition, there is SAS (Serial Attached SCSI) as an interface for connecting multiple storage mediums. With SAS, a plurality of devices are connected with SAS expanders. Even a greater number of storage mediums can be connected by connecting the expanders in multiple tiers, and a large number of storage mediums can be connected inexpensively in comparison to conventional interfaces. Meanwhile, an expander is a semiconductor having a logical function, and is vulnerable to failure caused by malfunction or noise. In a configuration where multiple storage mediums are connected with expanders arranged in series, if a certain expander is subject to failure, the storage mediums connected beyond the defective expander with the storage controller as the origin will become inaccessible even if those storage mediums are normal (operable). The redundancy of data will thereby deteriorate considerably.